1. Field of the Invention
This invention relates to the base catalyzed anionic polymerization of lactams and, more particularly, to reinforced polylactams in which an initiator precursor is coupled to the surface of the filler.
2. Description of the Prior Art
The use of fillers in polymeric systems is old and well known. At the one extreme fillers are used as diluents to make the polymer less expensive. At the other extreme fillers are used to enhance the physical properties of the polymer. Broadly speaking, fillers may be considered any foreign material in the polymer but, for purposes of this invention, the word "fillers" is used to mean particulate inorganic matter, such as minerals and glass fibers, having surfaces that are chemically reactive with silicate ester coupling agents.
The term "reinforced polymers" has many nuances ranging from one indicating that the filler material is bound by covalent bonds to the polymeric chain to one which merely indicates that the filler material contributes to a significant beneficial increase in physical properties of the polymer. The reinforced polylactams as disclosed in this specification embrace both of these definitions.
The prior art recognizes that polylactams can be reinforced with fillers by use of chemical coupling agents that have two reactive end groups. One of these end groups is effective to bond to the filler and the other end group is effective to react, during polymerization, to the polymerizing chain either along its backbone or by terminating the polymeric chain. Chemical coupling agents of this type are disclosed, for example, in U.S. Pat. Nos. 3,410,831; 3,341,501 and 3,418,268. Of the chemical coupling agents that have, in practice, been most frequently utilized are those of the type in which one end group is a silicate ester that is reactive with the surface of the filler particle and the other end group is an amine which will react to terminate the polymerizing chain. Typical of these coupling agents are silicate ester amines commonly used as sizing for fiberglass such as triethoxysilyltrimethyleneamine sold by Dow Corning under its trade designation A-1100.
The coupling system used in the prior art to reinforce polylactams can make useful contributions to the physical properties of polylactams but variously suffer from the fact that the reaction with the growing polymeric chain to form pendant groups may be random or erractic and, to the extent that they form a terminal group, limit the desired degree of polymerization.